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83361
SS18-SSX2 fusion. Unfortunately, RT-PCR results may be equivocal or falsely negative due to many
reasons such as when the available RNA is of poor quality or if a rare translocation partner is present. In
these cases, FISH testing can be used to identify 18q11.2 SS18 gene rearrangements in these tumors,
which supports the diagnosis of SS.
Useful For: As an aid in the diagnosis of synovial sarcoma when RT-PCR results are equivocal or do
not support the clinical picture
Interpretation: A neoplastic clone is detected when the percent of cells with an abnormality exceeds
the normal cutoff for the SYT FISH probe. A positive result suggests rearrangement of the SYT gene
region at 18q11.2 and supports the diagnosis of synovial sarcoma (SS). A negative result suggests no
rearrangement of the SYT gene region at 18q11.2. However, this result does not exclude the diagnosis of
SS.
Reference Values:
An interpretive report will be provided.
Clinical References: 1. Sandberg AA, Bridge JA: Updates on the cytogenetics and molecular
genetics of bone and soft tissue tumors. Synovial sarcoma. Cancer Genet Cytogenet 2002 Feb;133(1):1-23
2. Kokovic I, Bracko M, Golouh R, et al: Are there geographical differences in the frequency of
SYT-SSX1 and SYT-SSX2 chimeric transcripts in synovial sarcoma? Cancer Detect Prev
2004;28(4):294-301
Synovial Sarcoma by Reverse Transcriptase PCR (RT-PCR),
Paraffin
Clinical Information: Synovial sarcomas account for 9% to 10% of soft tissue tumors. These tumors
occur in 2 major forms: biphasic and monophasic. Monophasic tumors are composed entirely of spindle
cells, while biphasic tumors have epithelial cells arranged in glandular structures and mixed with spindle
cells. The tumors are usually positive for keratin and epithelial membrane antigen as well as vimentin by
immunostaining. Synovial sarcoma is a member the small-round-cell tumor group that includes
rhabdomyosarcoma, lymphoma, Wilms tumor, Ewing sarcoma, and desmoplastic small-round-cell tumor.
While treatment and prognosis depend on establishing the correct diagnosis, the diagnosis of sarcomas
that form the small-round-cell tumor group can be very difficult by light microscopic examination alone,
especially true when only small needle biopsy specimens are available for examination. The use of
immunohistochemical stains (eg, keratin and EMA) can assist in establishing the correct diagnosis, but
these markers are not entirely specific for synovial sarcoma. Expertise in soft tissue and bone pathology
are often needed. Studies have shown that some sarcomas have specific recurrent chromosomal
translocations. These translocations produce highly specific gene fusions that help define and characterize
subtypes of sarcomas and are useful in the diagnosis of these lesions.(1-4) Cytogenetic studies have
shown a distinctive chromosomal translocation, t(X;18)(p11;q11), in more than 90% of synovial
sarcomas. Cloning of the translocation breakpoint showed that t(X;18) results in the fusion of 2 genes
designated as SYT (at 18q11) and SSX (at Xp11). Two closely related genes, SSX1 and SSX2, have 81%
homology in proteins. SYT-SSX2 is present in 35% of cases. Patients with SYT-SSX2 translocation
usually have greater metastasis-free survival than those with SYT-SSX1. These fusion transcripts can be
detected by reverse transcriptase PCR (RT-PCR), by FISH, chromogenic in situ hybridization (CISH), or
by classical cytogenetic analyses. The RT-PCR and FISH procedures are the most sensitive methods to
detect these fusion transcripts.(3)
Useful For: Supporting a diagnosis of synovial sarcoma
Interpretation: A positive result is consistent with a diagnosis of synovial sarcoma. Sarcomas other
than synovial sarcoma, and carcinomas, melanomas, and lymphomas are negative for the fusion products.
A negative result does not rule out a diagnosis of synovial sarcoma.
Reference Values:
Negative
Clinical References: 1. Crew AJ, Clark J, Fisher C, et al: Fusion of SYT to two genes SSX1 and
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